Method for producing a mechanical stress detecting device

ABSTRACT

Herein disclosed is a method for manufacturing a mechanical stress detecting device using a block of laminated magnetic plates and a pair of non-magnetic side plates between which the block of the laminated magnetic plates is tightly interposed. The block of the magnetic plates and the side plates attached thereto have formed therein four apertures extending from one of the side plates to the other and symmetrically spaced apart from each other at an angle of about 90*, the apertures being located in a manner to have the phantom lines joining diametrically opposed pairs of the apertures are angled at about 45* to the direction in which a mechanical stress is applied to the block of the laminated magnetic plates. The detecting device is produced by heating the block of the laminated magnetic plates tightened by the side plates to the Curie point with a magnetizing coil passed through one pair of apertures in the block and cooling the block of the laminated plates through a predetermined range of temperature with the magnetizing coil kept energized, whereby a magnetic core having a monoaxial magneto-anisotropy is obtained. The magnetizing coil is then removed and a detecting coil is passed through another pair of apertures in the block.

United States Patent [191 Nishimura June 12, 1973 METHOD FOR PRODUCING AMECHANICAL STRESS DETECTING [73] Assignee: KabushikiKaisha Meidensha,

Tokyo, Japan 22 Filed: May 15,1972 21 App]. No.: 253,598

Related U.S. Application Data [62] Division of Ser. No. 89,175, Nov. 13,1970.

[30] Foreign Application Priority Data 336/20, 218, 234; 73/141 A, DIG.2; 317/143; 148/103, 108

[56] References Cited UNITED STATES PATENTS 2,895,332 7/1959 Dahle etal. 73/DlG. 2 X 3,158,516 11/1964 Walter et al. 148/108 3,307,405 3/1967Stucki 73/DlG. 2 X

Primary Examiner-Charles W. Lanham Assistant ExaminerCarl E. HallAttorney-Hans Berman and Kurt Kelman [5 7] ABSTRACT Herein disclosed isa method for manufacturing a mechanical stress detecting device using ablock of laminated magnetic plates and a pair of non-magnetic sideplates between which the block of the laminated magnetic plates istightly interposed. The block of the magnetic plates and the side platesattached thereto have formed therein four apertures extending from oneof the side plates to the other and symmetrically spaced apart from eachother at an angle of about 90", the apertures being located in a mannerto have the phantom lines joining diametrically opposedpairs of theapertures are angled at about 45 to the direction in which a mechanicalstress is applied to the block of the laminated magnetic plates. Thedetecting device is produced by heating the block of the laminatedmagnetic plates tightened by the side plates to the Curie point with amagnetizing coil passed through one pair of apertures in the block andcooling the block of the laminated plates through a predetermined rangeof temperature with the magnetizing coil kept energized, whereby amagnetic core having a monoaxial magnetoanisotropy is obtained. Themagnetizing coil is then removed and a detecting coil is passed throughanother pair of apertures in the block.

3 Claims, 10 Drawing Figures PATENIEB J11!" 3973 SHEEI1BF3 FIG PATENIED1 FIG.5

illvll METHOD FOR PRODUCING A MECHANICAL STRESS DETECTING DEVICE This isa divisional application from the applicants copending application Ser.No. 89,175 filed Nov. 13, 1970.

The present invention relates generally to a method for producing adevice for detecting and measuring a mechanical stress or pressure and,more particularly, to a method for producing device which is adapted toconvert a mechanical stress or pressure into a corresponding variationin an electrical quantity representing a magneto-strictive force in amagnetic material for quantitatively detecting the mechanical stress orpressure. The device of this nature will prove advantageous for themeasurement of various weights and mechanical pressures in numerousquarters of the industry.

The device to which the present invention is directed is basically ofthe type which is disclosed in the Japanese Pat. Publication No. 31-495issued under the date of Jan. 27, 1947. The device described thereincompRises a plurality of closely laminated magnetic plates and a pair ofside plates which are securely mounted on both sides of the block of thelaminated magnetic plates by means of bolts. The magnetic plates and thesides plates which are thus integral with the block of the magneticplates form an integral magnetic core. Four separate apertures extendthrough the magnetic plates and the side plates. The apertures arespaced at 90 from each other so that there are two pairs of apertureswhich are opposite to each other. An exciting coil is passed through afirst pair of opposite apertures and a detecting coil is passed througha second pair of opposite apertures. The exciting coil and the detectingcoil are thus in a crossing relationship on both sides of the magneticcore. The exciting coil is connected to a source of an ac power. Formeasurement of a mechanical stress or pressure, the load is applied tothe magnetic core in a direction perpendicular to the direction in whichthe magnetic plates are laminated, viz., at an angle of about 45 to thedirections in which the exciting and detecting coils cross each other,whereby a signal having a magnitude which is indicative of the loadapplied to the magnetic core is produced from the detecting coil.

The magnetic core to be used in this type of detecting device isgenerally made of a material which is magnetically non-directive orwhich is free from a residual strain, because of the fact that themagnetic characteristics of the core are otherwise subject toimpairement by the residual strain in the laminated magnetic plates perse or by the residual strain which is induced in the process oflaminating the magnetic plates. If, in this instance, a magneticallydirective material is used, then the resultant magnetic core is mostresponsive to the applied load in the direction in which the directionof the spontaneous magnetization or of the monoaxial magnetic anisotropyis 45 to the direction of the load applied. This phenomenon can beascertained and proved theoretically. The present invention thuscontemplates significantly increasing the apparent detection sensitivityin the quantitative detection of a mechanical stress or pressure throughutilization of such phenomenon.

The material to form the magnetic core is usually produced in twodifferent methods, one being the cold rolling and the other being thecooling in a magnetic field.

To produce the magnetic core material in the cold rolling method, it isrequired that the monoaxial magneto-anisotropic material have asufficient adaptability to rolling. Moreover, the cold-rolled magneticmaterial is so thin that the magnetic core made up of the laminatedplates of such thin material can not be free from deformation due toapplication of a load in a direction perpendicular to the direction inwhich the plates are laminated on each other. Where a pair of sideplates are secured to both sides of the block of the laminated magneticplates by means of bolts or other suitable tightening means, themagnetic core is subject to a mechanical distorsion resulting from thepressure exerted from the side plates. If it is desired to remove suchmechanical distorsion by heating the magnetic core, the monoaxialmagnetic anisotropy which haS been attained through coil rolling isimpaired and, as a result, the magnetic core is no longer acceptable foruse in the detecting device of the type to which the present inventionappertains.

When, on the other hand, a certain type of magnetic material such as forexample a sufficiently deoxidized permalloy containing about 63 percentnickel has been heated in a magnetic field to a temperatureapproximating the Curie point, say about 600 C, is cooled down through arange of about 250 C in the magnetic field, then the crystal magneticanisotropy of the cubic crystals is caused to disappear if the magneticmaterial is cooled at a selected rate such as about 10 C/hour and amonoaxial magnetic anisotropy is induced in the direction of themagnetic field which has been built up at the initial elevatedtemperature. As the cooling proceeds, the directions of the magnetism inthe individual magnetic domains are oriented and fixed in the directionof the magnetic field in which the magnetic material is placed. Where aplurality of magnetic plates of the thus produced monoaxialmagneto-anisotropic material are laminated into a unitary block and apair of side plates are mounted under pressure on both sides of theblock of the laminated plates so as to form an integral magnetic core, amechanical strain is Produced in the magnetic core similarly to themagnetic core made up of laminated plates manufactured by cold rolling.This difficulty will be avoided if a core having Previously laminatedmagnetic plates which are integral with side plates is cooled in amagnetic field so as to produce a magnetic core of monoaxialmagnetoanisotropic nature. For this purpose, the magnetic field may beproduced in such a manner that the magnetic core having the laminatedplates secured to the side plates is placed in a heating over which issurrounded by a magnetizing coiland that the magnetizing coil is excitedwith an intense electric current. Since, in this instance, the magneticcore has a considerably large thickness, the magnetizing coil should beexcited with a practically inoperably high electric current so as toovercome the demagnetizing coefficient of the core. If, to avoid this,the magnetic plates separated From each other'are cooled in the magneticfield and are thereafter laminated upon one another, the performancecharacteristics of the resultant magnetic plates will be impaired Partlybecause of the mechanical distorsion of the magnetic core due to thetightening pressure from (the side plates and partly because of thestructural sensitivity of the magnetism of the material used. If, fur- 3thermore, the magnetic plates are laminated and the side plates aresecured thereto by the use of a suitable adhesive material without usingbolts, the resultant magnetic core will be invariably subject tomechanical distorsion due to the deforming stress to be exerted when theadhesive material is being set and, as such, the problem as hereinbeforepointed out is still maintained.

In order to solve this and other problems, I have proposed in theaforesaid copending application a device which comprises a magnetic coreincluding a block of a plurality of closely laminated magnetic platesand a pair of side plates which are securely mounted on both sides ofthe block. The magnetic core has formed therein four apertures extendingthrough the block of the magnetic plates in a direction which issubstantially perpendicular to the plates and spaced apart substantiallysymmetrically from each other at an angle of about 90. These aperturesare disposed in such a manner that phantom lines joining the respectivediametrically opposed pairs of the apertures are angled at about 45 to adirection in which a load to be detected is applied to the magneticcore. The detecting device further comprises an exciting coil which ispassed through one of the pairs of the apertures and which is connectedto a source of an ac power and a detecting or output coil which ispassed through the other of the pairs of the apertures. These excitingand detecting coils are positioned in amanner to cross each other on theouter surface of either of the side plates at an angle of about 45 tothe direction of the load to be applied to the magnetic core. Thismagnetic core is bestowed with a monoaxial magnetic anistropy which hasbeen established by cooling the magnetic core from an elevatedtemperature through a certain range in a magnetic field.

The present invention is thus concerned with a method which isspecifically adapted to produce the detecting device having the aboveoutlined general construction. The method according to the present in-.vention generally comprises the steps of laminating a plurality ofmagnetic plates upon each other into an integral block, securelymounting a pair of side plates to both sides of the block by means offastening means for forming an integral magnetic core, the core havingformedv therein four apertures extending through the magnetic core in adirection substantially perpendicular to the laminated plates and spacedapart symmetrically from each other at an angle of about 90, themagnetic core, passing a magnetizing coil through one of the pairs ofthe apertures, the magnetizing coil being connected to a source of dcpower, placing the resultant magnetic core in a hot atmosphere, reducingthe temperature of the hot atmosphere through a predetermined range andat a predetermined rate while energizing the magnetizing coil from thesource of dc power for establishing a monoaxial magnetic anisotripy inthe magnetic core, removing the magnetic core from the hot atmosphere,removing the magnetizing coil from the magnetic core, passing anexciting coil through a first one of the pairs of the apertures andpassing a detecting coil through a second one of the pairs of theapertures.

Other objects, features and advantages of the method therefor accordingto the present inventionv will be more clearly understood upon perusalof the following description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a perspective view of a mechanical stress detecting device tobe produced in a method according to the present invention;

FIG. 2 is a side elevation of a block of magnetic plates forming part ofthe device shown in FIG. 1;

FIG. 3 isa schematic view showing an equivalent electric circuit of thedevice illustrated in FIG. 1;

FIG. 4 is a perspective view showing a magnetic core forming part of thedevice shown in FIG. 1;

FIG. 5 is a schematic view showing the conditions in which the magneticcore shown in FIG. 4 is being cooled in a magnetic field in the processof carrying out the method according to the present invention;

FIG. 6 is a graphic view showing dc magnetization characteristics curvesof the magnetic plate produced in the cooling process of FIG. 5;

FIG. 7 is also a graphic view showing the variation in the magnetizationcharacteristics of the magnetic plate caused by application of amechanical stress to the magneticrplate;

FIG. 8 is similar to FIG. 1 but now illustrates a modified form of thedevice shown in FIG. 1;

FIG. 9 is a graphic view showing a mechanical hysteresis loop of anelongation varying in terms of a mechanical stress; and

FIG. 10 is a graphic view showing an electrical hysteresis loop of anelectric output varying in terms of a mechanical stress.

Reference is now made to the drawings, more specifically to FIGS. 1 and2 which show the device which is to be produced in the method accordingto the present invention.

As illustrated, the device, designated generally by reference numeral10, includes an integral block 11 of a plurality of closely laminatedmagnetic plates 12 of contoured configuration. The magnetic plates 12are herein shown to have inboardly curved corners. A pair ofsubstantially identical side plates 13a, 13b of usually non-magneticmaterial are securely mounted on both sides of the block 11 of themagnetic plates 12 by means of suitable rigid fastening means such asbolts 14a, 14b, 14c, 14d as shown. The block 11 of the magnetic plates12 and the side plates 13a, 13b attached thereto thus form an integralmagnetic core which is generally represented by reference numeral 15 inFIG.

The magnetic core 15 thus formed has four apertures 16a, 16b and 17a,17b which extend through the block 11 of the laminated magnetic plates12 and the side plates 13a, 13b in a direction which is perpendicular tothe magnetic core as best seen in FIG. 4. The apertures 16a, 16b and17a, 17b are symmetrically spaced from each other at an angle of aboutand are disposed in such a manner that the lines connecting thediametrically opposite pairs of the apertures are angled at about 45 tothe direction in which a mechanical stress or load P is applied to themagnetic core 15 as indicated by an arrowhead in FIG. 1. Two separatecoils l8, 19 are passed through the respective diametrically oppositepairs of the apertures 16a, 16b and 17a, 17b. More specifically, anexciting coil 18 is passed through the apertures 16a, 16b and a stressdetecting coil 19 is passed through the apertures 17a and 17b. Theexciting and stress detecting coils 18 and 19, respectively, thus crosseach other on the outer surface of the side plate 130 at an angle ofabout 45 to the direction of the mechanical stress or load P. Themechanical stress detecting device according to the present invention isthus made up of the magnetic core comprising the block 11 of the closelylaminated magnetic plates 12 and the side plates 13a, 13b secured to theblock 11. The magnetic core 15 herein used has a monoaxialmagnetoanistropy which is established by field cooling with amagnetizing coil energized as will be discussed in more detail. Theexciting and stress detecting coils 18 and 19, respectively arepositioned in such a manner that the exciting coil lies in a plane whichis similar to the plane in which the magnetizing coil lay during thefield cooling process while the stress detecting coil lies in a planewhich is substantially normal to the plane in which the exciting coillies. Designated by reference numeral 20 is a source of an ac electricpower, which is connected to the magnetizing coil 18 to energize same. 1

An equivalent electric circuit of the device constructed as shown inFIG. 1 is illustrated in FIG. 3, wherein the L-shaped section 15corresponds to the magnetic core 15 which has a monoaxialmagnetoanisotropy established through cooling the magnetic core 15 in amagnetic field. The vertically elongated portion l5a.of this L-shapedsection 15 corresponds to the plane in which the exciting coil 18 lies,viz., the plane in which the magnetizing coil lay during the fieldcooling process. The magnetic characteristics resulting from thisparticular plane is indicated by a hysteresis loop a of FIG. 6 whichshows variations in a magnetoing the temperature in the heating oven 22from about 600 C through the region of about 250 C at the rate of about10 C per hour. The resultant magnetic core 15 is now provided with amonoaxial magnetic anisotropy. This magnetic core 15 is removed from theheating oven 22, whereupon the magnetizing coil 18 is removed from themagnetic core 15. The exciting coil 18 is now passed through theapertures 16a, 16b on the same plane of coiling as that of themagnetizing coil 18, while the stress detecting coil 19 is passedthrough the other diametrically opposite pair of apertures 17a, 17b.

In the method for producing the device in accordance with the presentinvention, the magnetic core 15 is annealed when being cooled in themagnetic field and the internal mechanical distorsion of the magneticcore is removed and the plastic deformation of the integrally combinedelements of the magnetic core is caused to add to the rigidity of thecore. In the process of cooling the magnetic core 15 in the magneticfield, a monoaxial magneto-anistropy develops along the closed magneticcircuits 23 in the magnetic plates 12 forming the magnetic core, asillustrated in FIG. 5. The

monoaxial magneto-anistropy is fixed in the magnetic core 15 as themagnetic core is cooled down. When, therefore, the magnetic core 15 isplaced on use at a normal temperature, an easy magnetization axis isestablished only in a direction parallel to the closed magnetic circuits23 so that the magnetic core 15 is capable of sensitively responding toan application thereto of a motive force H in terms of an ideal fluxdensity B. The

of the plane in which the stress detecting coil 19 lies,

viz., the plane substantially normal to the plane in which themagnetizing coil lay during the field cooling process of the methodaccording to the present invention. The magnetic characteristicsresulting from this particular plane are isoperm characteristics asindicated by a hysteresis loop b of FIG. 6.

The mechanical stress detecting device which has thus far been describedin detail is produced in the method according to the present inventionin the following manner. A plurality of magnetic plates 12 are firstlaminated upon one another, each of which magnetic plates has formedtherein four apertures 16a, 16b and 17a and 17b which are symmetricallyspaced from each other at an angle of about 90 and disposed in such amanner that the lines connecting the diametrically opposite pairs ofapertures are angled at about to the direction of the mechanical stressto be applied to the magnetic plates 12, as previously discussed. Theside plates 13a and 13b are rigidly attached to both sides of theresultant block 11 of the laminated magnetic plates 12 by the aid of thebolts 14a, 14b, 14c, 14d

thereby to form the integral magnetic core 15.

A magnetizing coil 18' is then passed through thevdiametrically oppositepair of apertures 16a and 16b and is connected to a dc power 21, asschematically illustrated in FIG. 5. The magnetic core 15 thus havingthe magnetizing coil 18 is now placed in a heating oven 22 which isfilled with a reductive atmosphere such as hydrogen gas. The magnetizingcoil 18' is then energized from the dc power source 22 with apredetermined demagnetizing current which is independent from thethickness of the magnetic core 15, while slowly reducmechanical stressor load.

FIG. 6 illustrates hysteresis loops of the magnetomotive force Hrelative to an ideal flux density B, wherein the loop a indicatesmagnetizing characteristics of the exciting coil 18 and the loop bindicates the magnetizing characteristics of the stress detecting coil19 having the plane of coiling which is perpendicular to the plane ofcoiling of the exciting coil 18. It will thus be appreciated that thecooling of the closely laminated magnetic plates in the magnetic fieldestablished by the closed magnetic circuits is advantageous because thecooling effect is not influenced by the demagnetizing field and,consequently that the cooling in the magnetic field can be carried outwithout respect to the thickness of the magnetic core 15 so as to permitthe use of a relatively low magnetizing current. I

When, in the device according to the present invention, the excitingcoil 18 is energized from the ac power source 20 with a stabilized acvoltage of a square or sinusoidal waveform and a mechanical stress, isapplied to the magnetic core 15, the magnetizing characteris- "tics ofthe ampere-turns NI with respect to the magnetic flux d) shifts from thesquare hysteresis loop a of FIG. 7 (which corresponds to the hysteresisloop a of FIG. 6) to the square hysteresis loop a of FIG. 7 indicated bya dotted curve. Since, however, the saturability characteristics arepractically not impaired, the magnetic core 15 can be usedsatisfactorily as a saturable reactor as will be discussed later. When,moreover, a stabilized ac voltage having a square or sinusoidal waveformis applied to the exciting coil 18 of the device according to thepresent invention, the quantity of the flux interlinking the detectingcoil 19 during applicadistribution. The detecting device according tothe present invention is, therefore, capable of providing a presentinvention which reduces the load to be applied to the operating electriccircuit to be used in connection with the detecting deviceand whichprovides an increased signal-to-noise ratio.

When, in operation, exciting coil 18 is excited from I the ac powersource 20 with a stabilized ac voltage having a sinusoidal or squarewaveform and the mechanical stress to be measured is applied to themagnetic core 15 in the direction of :the arrowhead in FIG. 1, then thefluxd; induced by the current flowing through the magnetizing coil 18is'subjected to a distorsion and consequently caused to intersect withthe stress detect-- ing coil 19 so that a voltage proportional to theapplied mechanical stress is produced by the stress detecting coil 19.The mechanical stress can be measured from thevoltage thus obtained.

FIG. 8 now illustrates a modified form of the stress detecting devicewhich is produced inaccordance with A the present invention. Themodified mechanicalstress detecting device 10' includes an integralblock 11 comprising a plurality of closely laminated magnetic plates 12and a pair of load-sharing members 24a and 24b each of which is made upof a plurality of laminated plates of a non-magnetic material and whichare mounted on both sides of the laminated magnetic plates. A pair ofside plates 13a, are securely mounted on both sidesof the thusconstructed block 11 by means of bolts 14a, 14b, 14c, 14d asillustrated. The block ll'of the laminated magnetic plates 12 and theload-sharing members 24a and 24b thus form an integral magnetic core15'. W v, I g g The magnetic core 15' thus constructed has four,apertures 16a, 16b and, 17a, 17b which extend through the block 11 ofthelaminated magnetic plates 12 and the load-sharing members 24a and 24bin the direction of thickness of the magnetic core 15'. The apertures16a, 16b and'l7a, 17b are symmetrically-spaced from each other at anangle of about 90 and are disposed in such a manner that the linesconnecting the diametrically opposite two pairs of the apertures areangled at about45 to the direction of the load P to be applied to themagnetic core 15 as indicated by an arrowhead in FIG. 8. An excitingcoil 18 is passed through one diametrically opposite pair of theapertures 16a, 16b and a stress detecting coil 19 is passed through theother diametrically opposite pair of the apertures-17a, 17b. Theexciting and detecting coils l8 and 19, respectively, thus cross eachother on the outer surface of the side plate 13a at an angle of about 45to the direction of the load P. The modified mechanical stress detectingdevice shown in FIG. 8 is thus essentially similar to the device shownin FIG. 1 except for the-provision of the load-sharing members 24a and24b and, as such, the

modified device has an equivalent electric circuit which is common tothe circuit shown in H6. 3. Furthermore, the magnetic core 15' of themodified stress detecting device has a monoaxial magnetic anisotropy'which is attained by cooling the magnetic core in a magnetic field,similarly to the device shown in FIG. 1.

The device shown in H6. 8 is, according to the present invention,produced in the following manner. A

plurality of magnetic plates 12 are first laminated upon each other, andthe loadsharing members 24a, 24b are attached to both sides of thelaminated magnetic plates 12 so as to form an integral block 11'. Theside plates 13a and 13b are then mounted securely on both sides of thethus constructed block 11' by means of the bolts 14a, 14b; 14c, 14d,thereby constituting an integral magnetic core 15'. The magnetic core 15has formed therein four apertures 16a, 16b and 17a, 17b which aredisposed in a manner previously discussed."

A magnetizing coil 18' is passed throughthe diametrically opposite pairof the apertures 16a, 16b and is connected to a dc power source 21 asschematically illustratedin FIG. 4. The magnetic core 15' thus providedwith the magnetizing coil 18' is placed in a heating oven 22 which isfilled with a suitable reductive atmosphere such as hydrogengas. Themagnetizing coil 18is then energized fromthe dc power source 21 with apredetermined magnetizing current which is independent from thethickness of the magnetic core 15', while reducingthe temperature in theheating, oven 22 through a region of about 250 C from about 600. Cpreferably at the rate of about 10", C per hour. The resultant magneticcore 15 has a monoaxial magnetic anisotropy. The magnetic core 15' isnow removed from the heating oven 22, whereupon the magnetizing coil 18'is removed from the magnetic core 15'. The exciting coil 18 is thenpassed through the apertures 16a, 16b and thereafter the stressdetecting coil 19 is passed through the apertures 17a, 17b. It isapparent that the device shown in FIG. 8 is capable of detecting as avoltage signal a considerably great mechanical stress or such a great.mechanicalstress. To provide the magnetic core with desiredcharacteristics as previously discussed, furthermore, the material to beusable as the magnetic core is necessarily limited to a costly materialsuch as for example a 63 percent Permalloy. The use of such a costlymaterial in a large quantity is apparently objectionable from theeconomical point of view.

The provision of the load-sharing members 24a and 24b as in theembodiment shown in FIG. 8 is advantageous in this particular respectbecause only a limited number of magnetic plates 12 is used incombination with less costly non-magnetic plates forming the loadsharingmembers 24a and 24b. The material usable as the non-magnetic plates maybe stainless steel containing 18 percent chrome and 8 percent nickelwhich is commercially readily available at a low cost. The number of thecomponent plates of the load-sharing members may be selected independence with the magnitude of the load to be applied to the magneticcore. The load-sharing members 24a, 24b serve not only to reduce theproduction cost of the magnetic core but to carry a portion of the loadapplied to the magnetic core this instance, the same voltage may beproduced without regard to the difference between the numbers of thenon-magnetic plates which are used in the two detecting devices, theamounts of the loads measured will be exactly determined by properlygraduating the measuring scale or through appropriate conversion of theoutput voltages with use of suitable parameters. Provision of theload-sharing members 24a and 24b is, in this manner, conductive not onlyto reducing the production cost of the magnetic core but tostandardization of the detecting device for the loads to be detected.

To save the load to be directly imparted to the laminated magneticplates 12, it may be also advantageous to have the upper and lower endsof the side plates 13a, 13b flush with the upper and lower surfaces,respectively, of the block 11, if desired, as illustrated in FIG.

8. The side plates 13a, 13b being configured in this manner, the load tobe measured is shared not only by the block 11' but by the side plates13a, 13b so as to reduce the load to be imparted to the laminatedmagnetic plates 12. This is also advantageous because the mechanical andconstructional hysteresis resulting from the load cycles, viz., thehysteresis e in terms of the mechanical stress aas shown in FIG. 9 andaccordingly the electrical hysteresis in the output voltage v in termsof the load p as shown in FIG. can be avoided. Unless, therefore, theupper and lower ends of the side plates 13a, 13b are flush with theupper and lower surfaces, respectively, of the block 11, then the sideplates may not be functionally completely integral with the magneticcore 11 with the result that an unusual shearing stress may be built upbetween the side plates 13a, 13b and the block 11 of the laminatedmagnetic plates 12 and the load-sharing members 24a, 24b even though theload cycles are limited within the presumed limit of elasticity. Suchunusual shearing stress will cause a frictional heat between the sideplates 13a, 13b and the block 11', resulting in the mechanical andelectrical hystereses as above mentioned.

The stress detecting device constructed as shown in FIGSJ and 8 andproviding the hereinbefore discussed outstanding features may findapplications in various fields of the industry for the purpose ofmeasuring various weights, pressures and other mechanical stresses,although examples of such practical applications of the device are notherein described.

What I claim is:

l. A method for producing a device for quantitatively detecting amechanical stress comprising the steps of laminating a plurality ofmagnetic plates upon each other into an integral block, securelymounting a pair of side plates to both sides of said block by means offastening means for forming an integral magnetic core, said core havingformed therein four apertures extending through said magnetic core in adirection substantially perpendicular to said plates and spaced apartsymmetrically from each other at an angle of about said apertures beingdisposed to have phantom lines interconnecting respective diametricallyopposite pairs of the apertures angled at about 45 to the direction inwhich a mechanical stress to be detected is applied to said magneticcore while in use, passing a magnetizing coil through one of said pairsof the apertures, said magnetizing coil being connected to a dc powersource, placing the resultant magnetic core in a hot atmosphere,reducing the temperature of said atmosphere through a predeterminedrange and at a predetermined rate while energizing said magnetizing coilfrom said dc power source for establishing a monoaxial magneticanisotropy in said magnetic core, removing the magnetic core from saidatmosphere, removing said magnetizing coil from said-magnetic core,passing an exciting coil through said one of said pairs of theapertures, and

passing a detecting coil through the other of said pairs of theapertures.

2. A method for producing a device for quantitatively detecting amechanical stress comprising the steps of laminating a plurality ofmagnetic plates upon each other, mounting a pair ofIOad-Sharing memberson both sides of said plurality of magnetic plates for forming anintegral block, each of said load-sharing members being made up of aplurality of laminated nonmagnetic plates, securely mounting a pair ofside plates on both sides of said block by means of fastening means forforming an integral magnetic core, said magnetic core having formedthe-rein four apertures extending through said corein a directionsubstantially perpendicular to said plates and spaced apartsymmetrically from each other at an angle of about 90, said aperturesbeing disposed to have phantom lines inter-connecting respectivediametrically opposite pairs of the apertures angled at an angle ofabout 45 to the direction in which a mechanical stress to be detected isapplied to said magnetic core while in use, passing a magnetizing coilthrough one of said pairs of the apertures, said magnetizing coil beingconnected to a source of dc power, placing the resultant magnetic corein a hot atmosphere, reducing the temperature of said atmosphere througha predetermined range and at a predetermined rate while energizing saidmagnetizing coil from said source of dc power for establishing amonoaxial magnetic anisotropy in said magnetic core, removing themagnetic core from said atmosphere, removing said magnetizing coil fromthe magnetic core, passing an exciting coil through said one of saidpairs of the apertures and passing a detecting coil through the other ofsaid pairs of the apertures.

3. A method as claimed in claim 1, wherein said atmosphere is heated tothe vicinity of the Curie temperature..

1. A method for producing a device for quantitatively detecting amechanical stress comprising the steps of laminating a plurality ofmagnetic plates upon each other into an integral block, securelymounting a pair of side plates to both sides of said block by means offastening means for forming an integral magnetic core, said core havingformed therein four apertures extending through said magnetic core in adirection substantially perpendicular to said plates and spaced apartsymmetrically from each other at an angle of about 90*, said aperturesbeing disposed to have phantom lines interconnecting respectivediametrically opposite pairs of the apertures angled at about 45* to thedirection in which a mechanical stress to be detected is applied to saidmagnetic core while in use, passing a magnetizing coil through one ofsaid pairs of the apertures, said magnetizing coil being connected to adc power source, placing the resultant magnetic core in a hotatmosphere, reducing the temperature of said atmosphere through apredetermined range and at a predetermined rate while energizing saidmagnetizing coil from said dc power source for establishing a monoaxialmagnetic anisotropy in said magnetic core, removing the magnetic corefrom said atmosphere, removing said magnetizing coil from said magneticcore, passing an exciting coil through said one of said pairs of theapertures, and passing a detecting coil through the other of said pairsof the apertures.
 2. A method for producing a device for quantitativelydetecting a mechanical stress comprising the steps of laminating aplurality of magnetic plates upon each other, mounting a pair ofload-sharing members on both sides of said plurality of magnetic platesfor forming an integral block, each of said load-sharing members beingmade up of a plurality of laminated non-magnetic plates, securelymounting a pair of side plates on both sides of said block by means offastening means for forming an integral magnetic core, said magneticcore having formed therein four apertures extending through said core ina direction substantially perpendicular to said plates and spaced apartsymmetrically from each other at an angle of about 90*, said aperturesbeing disposed to have phantom lines inter-connecting respectivediametrically opposite pairs of the apertures angled at an angle ofabout 45* to the direction in which a mechanical stress to be detectedis applied to said magnetic core while In use, passing a magnetizingcoil through one of said pairs of the apertures, said magnetizing coilbeing connected to a source of dc power, placing the resultant magneticcore in a hot atmosphere, reducing the temperature of said atmospherethrough a predetermined range and at a predetermined rate whileenergizing said magnetizing coil from said source of dc power forestablishing a mono-axial magnetic anisotropy in said magnetic core,removing the magnetic core from said atmosphere, removing saidmagnetizing coil from the magnetic core, passing an exciting coilthrough said one of said pairs of the apertures and passing a detectingcoil through the other of said pairs of the apertures.
 3. A method asclaimed in claim 1, wherein said atmosphere is heated to the vicinity ofthe Curie temperature.